I recently experienced a coolant “leak” but I cannot figure out the source. I have a 1969 Hurst with the original stock 455. In the past 6 months I have had the cooling system flushed, new radiator installed, new heater core and hoses, and a new thermostat and bypass hose. Shroud and rubber seal seem to be ok. A coolant overflow tank was added by the previous owner. A new radiator cap rated to 15lbs was installed a few months ago. The system seemed to be functioning well, the liquid level in the tank going down as the system cooled and going up as the system got hotter. Always staying between the upper and lower-level lines. No leaks. At temperature the upper hose was very firm and the system appeared to be holding pressure. On hot days, It ran between 200- 230F depending on conditions, and if the AC was on.

In Houston it has been over 100F for 50+ days, so the car was not driven. It how now cooled to 95-97F so I decided to take it out, and, run the air conditioning- yep playing with fire. I watched the temperature gauge, and it ran between 220-230F. When parked, the temp would go up to slightly over 240F. But usually, I was not parked for more than about 15 minutes. The temperature would go down when I started driving. So, I got home and parked the car. About 30-45 minutes later I went outside and saw liquid on the driveway under the car and saw coolant on the bezel below the headlights. I opened the hood and there was coolant around the front of the engine, fenders, hood, intake manifold, etc. I noticed that the coolant tank still had some coolant in the bottom, and when I squeezed the upper hose fluid would flow in/out of the tank. I waited until the system was cool enough to open the radiator, and the radiator was full to the top. I restarted the car, did not notice any leaks, the upper hose firmed up under pressure, so I put the car in the garage. Several hours later I checked again, the radiator was full, but the tank had very little coolant, much like it was when it spewed coolant earlier. It looks like I lost the contents of the tank- about 16 ounces(?), in the initial eruption.

Now the only thing I can see that is different from the start of the drive, is the cap on the coolant tank is covered in a gray/white material that must be lightly scraped to be removed. That material was not there before i started driving. It looks like the radiator overflowed the tank and the coolant spewed out of the vent hole in the coolant tank cap. Is it possible that while sitting outside without the benefit of coolant circulation and a fan, the coolant was heated up by the block until the pressure overcame the 15 lb. radiator cap? Could the radiator cap be faulty? I cannot see any other leaks, nor is there coolant on the garage floor. Is this normal behavior? Should my coolant tank have an overflow drain to the ground? Add an thermostat controlled electric fan that keeps running for a while when the car is turned off? I am stumped.

Sorry for the long write-up, but the details may save some questions.

 

First of all 220-230 is too hot for that car. I would not want to drive it much like that. I would not want to see anything over 200 on a regular basis. The stock thermostat shows to be 195.

The cap could certainly be defective. The temperature definitely will go up some after shutting the engine off. All of my listings show a 16lb cap ? One pound shouldn't make a big difference but if you are going to replace it make sure and get the correct one.

What fan are you using ? If it is a clutch type fan try shutting the engine off once it is fully warmed up and run out quickly and see if you can turn the fan by hand. When it is hot it should be fairly hard to turn . Or if you have a helper get the engine good and hot, open the hood and have them shut the engine off. If the fan keeps spinning then the clutch is probably worn out and not working.

 

The white crap is from Water Wetter additive

 

What temperature gauge did you use? If it's a reputable aftermarket temperature gauge (AutoMeter) and it reached 240° you might want to do a compression test.

 

Did the running hot start after the listed work was done or was the work done in an attempt to resolve the running hot?

How was the cooling system flushed with plain water or with chemicals?

Confirm that the coolant is at most a 50/50 ratio of coolant to water.

 

[QUOTE=Olds64;152327... you might want to do a compression test ... [/QUOTE]
... and/or pressure test the cooling system.

 

I was having a similar issue with my car. It would run fairly consistent around 190, but would puke big time once I shut it off. Turned out to be a bad radiator cap.

 

I want to thank everyone for the great advice.
The whole repair process started because I wanted to recommission the AC system which had not work in 20+ years according to the previous owner. Being in Houston, I knew the cooling system needed to be top notch to handle the heat and AC. Before I undertook the work on the cooling system, the car did run at about the same temp it does now. The cooling system was flushed with chemicals when I first got the car in May 2022, before I started the repairs later in the year.
I have an aftermarket temperature gauge. Based on the thermostat opening temp and the reading on the gauge when it opens, and the occasional test against an IR thermometer, it seems pretty accurate. The thermostat is a Mr. Gasket 180F 4364 High Performance Thermostat. The coolant is a 50/50 mix as I buy it pre-mixed. One bottle of Water wetter was added. I don't recall the brand. I checked the radiator cap it is a 16 Lb RC 27.

The cooling system was flushed with chemicals when I first got the car in May 2022. Later, before repairs were performed, the heater core was leaking. The bypass hose and thermostat housing were both leaking. Decided to replace thermostat while I repaired the leak in the housing and hose. I replaced the radiator as it was very rusty and the fact that I would be using the AC. Even after flushing from what I could see inside, it did not look very good. So, I now have a 4-row aluminum radiator.

I need to check the fan clutch. It does get firmer when hot but does spin about half a revolution when spun by hand when hot. How firm should the fan clutch be when hot? If I need a replacement- what is the recommended?

Thanks

 

I suspect this has something to do with your issue.
4 row aluminum? 1 or 2 row typically work very well.

 

I appreciate you've spent significant $$, time & effort in addressing some issues & upgrades. However, as I read through this thread, the singular item which stands out more than any other is the radiator cap since your coolant pukes AFTER you turn the car OFF.

Very first consideration is to purchase a new radiator cap ($10.00). They make many types of radiator caps & they're made by many manufacturers. Some of these manufactures make quality parts, some do not. Even a quality manufacturer can produce a part which is defective. I wouldn't waste another minute tracking down something else until I first evaluated your current radiator cap is the CORRECT & PROPER radiator cap for YOUR system.

 

Drain some coolant and then remove
​​​​the thermostat to look in the cooling system, unless it looks excellent I'd treat it with CRC ThermoCure to know it is clean. A few months ago we did a long, long list of repairs/changes to a #'s matching high end classic due to overheating. CRC ThermoCure solved the problem, put it in and let it work (chelate) for days. Ours took 2 or 3 treatments but it worked very well.

You can see from the results in the replaced radiator some flushes don't get it done.

 

When I swapped my radiator w/ a new aluminum one a few years back, the cap that came with the radiator didn't fit properly, even though the neck was machined from billet. I purchased another cap from AutoZone and it fit better, but not perfect. Not sure about your radiator, but the neck on my alum radiator leaves a lot to be desired since it makes getting a good seal to the cap very finicky.

 

Do you know if the folks hired to do the cooling flush removed the drain plugs from the engine block? The plugs are a hard access, but necessary for a thorough flush. As rusty as your radiator was you may still have rust compacted around a few of the cylinders if the drain plugs didn't come out. Thermocure is one of the top rated rust eliminators, in my opinion.

Regarding the fan clutch. Run the engine until hot, stand where you can see the fan spinning then cut the engine off. If the fan continues to rotate more than 1/2 revolution you should be suspecious of the fan clutch. Additionally, the radiator cap is important, be certain it functions correctly.

I don't have a/c, but my 455 runs all day long in Georgia heat and hangs at roughly 190 when I test with IR at thermo neck. I use 50/50 coolant/water along with one bottle of water wetter, and flush with Thermocure (plugs removed) when doing flushes.

Hope this helps....

 

Operating temps over 210 are considered high. Engines will heat up more directly after they are turned off before cooling back down. Put your old rad cap back on.

 

A new radiator cap is not going to have any effect on it running at 220 to 230 degrees.

Hayden heavy duty fan clutches work well if you end up needing one. They run between 50 and 70 bucks. Also does your a/c use R12 or R134. 134 runs at higher pressures and you will have more heat in the condenser to shed. I ended up putting a 16” pusher electric fan in front of the condenser to help with this. My a/c runs colder at idle and it also helps manage the engine temps in stop and go traffic. Not saying to add a fan to fix it. My car runs between 190 and 200 without the fan on. It is wired to come on when the a/c is on (like a modern car) and it mainly keeps the a/c nice and cold in traffic. If it is running hot at idle and cools off at road speeds you definitely have a air flow issue.

 

I'm sorry but where did I say a radiator cap would have an effect at 220° or 230°F? A radiator cap which does not seat correctly and does not maintain pressure can allow coolant to puke when the engine is turned off as the temperature of the coolant increases after engine shutdown.

 

I use a 7 PSI cap and don’t have any issues. Based on that, I have to conclude the psi rating of the cap isn’t the problem with the OP’s issue.

 

quick clutch test.. Get the engine hot shut it off have someone hold a stick the the fan and start the engine. If he can hold the fan from spinning it's shot.

 

Thats a good way to cause an injury or damage the car.

 

There is a detailed procedure in the service manual explaining how to test the fan clutch. It doesn't involve sticking your hands in the fan, trying to stop it, or any of that nonsense.

Put a heavy blanket over the grille opening. Start the engine, leave it on high idle. Turn on the A/C, and let it run while monitoring the temp gauge. If the clutch of functional, you will hear a distinct change in fan noise as it engages The engine will “roar” when revved. Remove the blanket, let the engine idle. Eventually the fan roar will stop as the engine cools down and the fan disengages.

 

If you goog (testing clutch fan) a vid comes up showing how without hurting person or car

 

... and of course everything you see on the internet is safe and effective.

 

Tuff crowd... Good Luck on the overheating problem my bets on the fan clutch

 

More great advice to use on solving this problem.

I am re-flushing the system again, just to be sure. I will add Thermacure. I will try and pull the plugs. I doubt that place that flushed the radiator the first time pulled the engine plugs.
I checked the radiator again, now that I can see inside- it has two rows. The rows appear to be wider than normal, but the radiator core thinner than the original.
The shroud is about 1/2 in- 3/8 in away from the back of the radiator. The radiator is not as wide as the original, hence the gap. Do I need to adjust the shroud to fit right up against the radiator? Or is the small gap acceptable.
I am going to get another radiator cap. Pretty cheap fix.
The fan clutch seems to have issues. When the car is hot and then shut down the fan spins at least one more rotation. Also, I don't feel a great deal of air flow at idle through the radiator. So, it is probably shot. Another $50-60 is not bad.

Thanks for all the help.

 

The gap should be filled, adhesive backed foam stuck to the shroud should work. Any air that comes through the gap is air that didn't go through the radiator to help rid heat.

 

If your fan clutch is original and means anything to you it can be rebuilt. Kirk Connell Corvettes located in Florida did mine without issues. They have a web presence.

 

If a fan can be spun while cold, and spins to less than half a turn when hot, and is never locked up; it's good. All this can be done with the engine off.

 

To close this out from my side. I did a thorough flush with Thermocure- leaving it in for about 5 days with short drives each day. The water came out black-green, but with very little silt or large particles. Pulled the engine plugs. Nothing significant came out of the drains- good water flow. Moved the radiator closer to the shroud, it appears that the radiator core is not as wide as the original, hence the gap between the radiator and shroud. Replaced the radiator cap. Fan clutch did not seem to pull a lot of air so I replaced with a new Hayden 2747 HD. Out of the box the new fan clutch was much harder to rotate by hand than the old one. The old fan clutch had a date of 1979 on it, so, it was passed its expiry date. After getting it all together, I noticed much more air flow even at idle. I went for a drive, outside temp about 95F. On the street without AC on the car ran about 195-200F, on the highway about 190-195F. With the ac on, the street temp went up to about 200-210F and highway 195-200F. When I stopped and turned off the car, the temp went to 240F. There was no overflow, in fact I think the engine might still be a bit low on coolant. I will monitor the coolant level. The downside, the air flow with the new fan clutch is louder. I will take that over higher temperatures. I think the new fan clutch made the biggest difference.
I want to thank everyone for the great advice.

 

Good work, great news. Drive on!